Outlines of Dairy Bacteriology, 8th edition: A Concise Manual for the Use of Students in DairyingRussell, H. L. (Harry Luman)
Science
Outlines of Dairy Bacteriology, 8th edition: A Concise Manual for the Use of Students in Dairying
Russell, H. L. (Harry Luman)
Dairy microbiology
~Germ content of milk utensils.~ Naturally the number of bacteria found in
different milk utensils after they have received their regular cleaning
will be subject to great fluctuations; but, nevertheless, such
determinations are of value as giving a scientific foundation for
practical methods of improvement. The following studies may serve to
indicate the relative importance of the utensils as a factor in milk
contamination.
Two cans were taken, one of which had been cleaned in the ordinary way,
while the other was sterilized by steaming. Before milking, the udder
was thoroughly cleaned and special precautions taken to avoid raising of
dust; the fore milk was rejected. Milk drawn into these two cans showed
the following germ content:
No. bacteria Hours before
per cc. souring.
Steamed pail 165 28-1/2
Ordinary pail 4265 23
Harrison[6] has shown how great a variation is in the bacterial content
in milk cans. The utensils were rinsed with 100 cc. of sterile water and
numerical determinations of this rinsing water made. In poorly cleaned
cans, the average germ content was 442,000; in cans washed in tepid
water and then scalded--the best farm practice--54,000, and in cans
carefully washed and then steamed for five minutes, 880.
Another method used by the writer is to wash the utensil with 100 cc.
sterile wash water, using a sterile swab to remove dirt. Then repeat the
process twice or more with fresh rinsing waters, making plate cultures
from each. The following data were obtained from three such
determinations:
No. bacteria in different washings. Total No.
I. II. III. bacteria.
7,800,000 1,450,000 49,000 9,299,000
283,000 43,400 35,000 361,400
1,685,000 105,000 61,400 1,851,400
~Infection of milk in udder cavity.~ A frequently neglected but
considerable factor of infection is that which is attributable to the
bacteria which are present in the udder and which are removed in large
numbers during the milking process. An examination of the fore milk, i.
e., the first few streams from each teat, and that which is subsequently
withdrawn, generally reveals a very much larger number of organisms in
the fore milk.[7] Not infrequently will this part of the milk when drawn
under as careful conditions as possible, contain several score thousand
organisms per cc. If successive bacterial determinations are made at
different periods of the milking, as shown in the following experiment,
a marked diminution is to be noted after the first portion of the milk
is removed:
_Bacterial content at different periods of milking._
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